Apparatus for Connecting A Rotating Drive Rod String To A Downhole Assembly

ABSTRACT

A system for connecting and disconnecting a rod string from a downhole assembly in which a captured spline assembly is encased in a receiver attached to the downhole assembly and an on-off tool separating the rod string from the downhole assembly.

This application claims benefits of earlier filed provisionalapplication Ser. No. 61/752,157, filed on Jan. 14, 2013.

The present invention relates, in a general sense, to oil and gasproduction wells and, more particularly, to improved apparatus andmethods for connecting and disconnecting a downhole assembly, including,e.g., geared centrifugal pumps.

BACKGROUND OF THE INVENTION

1. Field of the Invention

In a typical production well, a downhole assembly is lowered to apredetermined depth where it is immersed in the fluid deposit. The pumpis driven by a power supply at the surface of the well, and a rod stringspans the distance between the power supply and the pump in order todrive the pump.

The geared centrifugal pump (GCP), among other devices, utilizes the rodstring to rotationally drive a downhole pump. In the case of the GCP,this rod string is run inside the production tubing after the pumpassembly has been run and set at the desired downhole location. Thecurrent method of connecting the rod string to the downhole assembly, sothat rotational force can be transmitted to that assembly, is via a malestab-in rod attached to the end of the drive rod string that fits into acompanion female receptacle in a receiver at the top of the downholeassembly.

This stab-in rod may have any one of several cross sectionconfigurations, among them a square, hex, spline or other cross sectionthat figs snugly into a like-shaped female receptacle in the receiver.The stab-in rod is not attached to the receptacle for tensional loadsand is of such length as to permit free movement vertically to adjust todifferential vertical movement between the rod string and the downholeassembly. The stab-in rod, via the drive rods, rotates the femalereceptacle, which is fixedly attached to the drive shaft that extendsthrough the upper seal section. In the case of the GCP, the drive shaftis attached tot he input shaft of a speed increasing transmission,which, in turn, drives the centrifugal pump.

An important disadvantage to this system of a male stab-in shaft and afemale receptacle is debris can, and usually will, collect in the femalereceptacle before the rod string is run, or when the rod string isremoved for service, making it somewhere between difficult to impossibleto re-engage the stab-in rod into the receiver.

The present invention addresses that problem by eliminating a femalereceiver that is open to the unwanted collection of receptacle cloggingdebris.

SUMMARY OF THE INVENTION

In the business of oil and gas production, time is literally money. Itis readily understood, therefore, that any difficulty in connecting therod string to the downhole assembly costs dearly.

With that understanding, it is clearly a great advantage of the presentinvention to the oil producer, to eliminate the prior art difficultiesexperienced when, as and if the female receptacle is in any wayimpaired, thereby increasing the difficulty in making the connection.

It is a further benefit of the present invention to provide a mechanism,and a method of operation, which enhances the ability of the producer toconnect the rod string with the downhole assembly.

Other objects and advantages of the present invention will becomeapparent to those skilled in the art from a reading of the followingDetailed Description Of The Preferred Embodiment when read in concertwith the drawings.

It will quickly become apparent that all of the drawings are pictorialrepresentations of the area in the production tubing wherein thedownhole assembly is engaged by the rod string and disengaged as needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of the upper portion of a downhole assembly with ashort section of connecting tubing, in the area of the connectionbetween a downhole assembly and a rod drive string, illustrating themechanics of the connection in a prior art embodiment, wherein a femalereceptacle extends upwardly and away from the downhole assembly and isengaged by a depending drive rod and stab-in shaft;

FIG. 2 illustrates, pictorially, the prior art embodiment with the driverod and stab-in shaft disengaged; leaving the female receptacle open forcollection of debris;

FIG. 3 is a view similar to that of FIG. 1, the difference being theFIG. 3 embodiment illustrates the structure which characterizes thepresent invention, wherein the connection between the downhole assemblyand the drive rod string is via a captured spline assembly fixed withinthe receiver component of the downhole assembly; wherein the drive rodstring is engaged with a male receiver shaft extending upward from thecaptured spline assembly via an on-off tool;

FIG. 4 illustrates, pictorially, the present invention with the driverod string disengaged from the captured spline assembly receiver shaft;

FIG. 5 is an enlarged detail of the receiver and the captured splineassembly as shown in FIGS. 3 and 4, sectioned in order to illustrate thedetail within the assembly housing;

FIGS. 6 a, b and c illustrate, pictorially, a sequence of downholeactivity, when one employs the FIGS. 3 and 4 embodiment, in which thedrive string is initially moved into position to engage and capture, viathe on-off tool, the receiver shaft extending upwardly from the receivercaptured spline assembly;

FIGS. 7 a and b are expanded views of the structure of FIGS. 3 and 4,providing detail of the on-off tool currently in use in downholeoilfield production equipment.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The following detailed description discloses, to those skilled in theart, a novel system for engaging a downhole assembly with a rod drivestring.

It will be observed in the prior art configuration in FIG. 1, whichillustrates the current practice in the industry, various elements of asystem to connect a downhole assembly 22 to a drive rod string are shownby numbers following by a prime sign. Drive rod 24′ is attached tosplined stab-in rod 23″,which is inserted into the female splinereceptacle 25′ in receiver 27′. Spline receptacle 25′ is mounted withinthe receiver 27′ via bearings 45′, such that rotation of the rod string24′ will be transmitted by receptacle 25′ to the transmission driveshaft 51′, which is fixedly attached to receptacle 25′. The downholeassembly is thereby rotationally connected to the drive string 24′.Arrows A indicate the direction of fluid flow in the production tubingand downhole assembly.

This connection system functions satisfactorily until maintenance orrepair calls for a disconnect and the stab-in rod is removed from thereceiver 27′, as shown in FIG. 2, and the upwardly facing female splinedreceptacle 25′ is, thus, open to the capture of downward moving debris,shown by arrows B.

As shown in FIGS. 3 and 4, and in accordance with the present invention,the debris-clogging problem of the open female splined receptacle 26′shown in FIG. 2, is eliminated by reversing the downhole rod-receiverelements of the connection and making the rod-end connector the femaleportion 47 f of an on-off assembly 47, and the receiver connector themale portion 47 m of the on-off assembly 47.

Accordingly, an exemplary embodiment is shown in FIG. 4, wherein the rodstring 24 is withdrawn from engagement with the receiver 27, bydisconnecting the on-off tool 47, and there is no open receptacle facingupwardly towards the surface into which the debris can collect, and thedebris, shown as arrows B, falls harmlessly past the receiver 27 whereit will settle into the flow channels past the receiver and upper sealsection and, most importantly, does not interfere with the connectionbetween the rod 24 and the receiver extension shaft 54.

There are principal advantages to the present invention whenoperationally attaching a rod string to a downhole assembly, and, theyare:

1) The rods can be run after the downhole assembly is installed;

2) The rod string is able to move vertically, freely, while still intorque transmitting connection with the downhole assembly;

3) The rod string can be detached and retrieved without requiring theretrieval of the downhole assembly.

Referring, once again, to FIGS. 3 and 4, a system is configured to showthe structure of the present invention in its most basic form. Thesystem consists of a receiver 27, which houses the captured splineassembly 25. Captured spline assembly 25 is connected rotationally andtorsionally to the transmission input drive shaft 51 and to the driverod string 24 via the receiver extension shaft 54 and the on-off tool47, shown in FIG. 3 in its connected state.

The receiver extension shaft 54 extends into, and is rotationallyconnected to, the captured spline assembly 25, which, in turn, isrotationally connected to the transmission drive shaft 51.

The captured spline assembly 25 is shown in more detail in the partialcross section shown in FIG. 5. Extension shaft 54 has the freedom ofsome vertical movement within the splined assembly housing 49, whileremaining in torsional and rotational connection to assembly housing 49.Receiver extension shaft 54 passes through a seal 52 to keep debris fromentering the receiver 27. The splined assembly housing 49 is mounted inseveral shaft bearings 45 and is free to rotate within said bearings,but does not have the freedom of vertical movement within the receiver27.

Referring to FIG. 5, the receiver extension shaft 54 is shown near thebottom of its possible vertical travel within the splined assemblyhousing 49, with the male splined portion 48 engaging the female splinedbore 46 of the assembly housing 49. Cushioning spring 43, at thedownhole end of the female splined assembly housing 49, is clearlyshown. The upward vertical travel of extension shaft 54 is limited bycollet 50, fixedly attached to shaft 54, which is larger in diameterthan the diametric restriction 53 at the uphole end of assembly housing49. Assembly housing 49 is mounted within the receiver 27 with bearings45 that allow free rotation of the housing, but restrict its verticalmovement within the receiver 27. The assembly housing 49 is rotationallyand torsionally attached to transmission draft shaft 51.

The receiver captured spline assembly 25 provides a torsional connectionbetween the drive rod string 24 and the transmission input drive shaft51, while also allowing relative vertical movement between the driveshaft 24 and the receiver 27 required for connection, disconnection andvertical adjustment of the rod drive string position during rod stringinstallation and normal operations.

FIGS. 6 a, b and c show, pictorially, the steps followed during theinstallation and engagement of the drive rod shaft 24 and the receivercaptured spline assembly described above. The downhole assembly is runin the hole on the production tubing T and set at the desired depth. Thedrive rods 24, with the female portion of the on-off tool 47 f, are runnear the expected depth of the connection with the male portion of theon-off tool 47 m (FIG. 6 a), and slowly eased down until the female halfof the on-off tool 47 f fully engages and locks with the male half 47 m,and the receiver extension shaft 54 is at the bottom of its travelwithin the receiver captured splined assembly (FIG. 6 b). The rods arethen pulled up just to the point where all of the weight of the rodstring is carried by the installation equipment at the surface (notshown), and then pulled another approximately 1.5 feet and hung off(FIG. 6 c). This will give the rods about 1.5 feet of relative downwardtravel and 1.5 feet of relative upward travel within the receivercaptured spline assembly without either tagging the cushioning spring43, or hitting the upward travel stop 50. This amount of freedom ofvertical travel should be sufficient to accommodate any expectedrelative vertical movement between the drive rod string 24 and thereceiver 27.

FIG. 7 a shows a side view of the on-off tool 47, in its fully engagedstate. FIG. 7 b shows a side view of the on-off tool, with the femaleportion 47 f disengaged from the male portion 47 m.

Having now described the invention with particularity, those skilled inthe art will be able to envision alternative elements to those describedto accomplish essentially the same purpose as those originally set forthherein. It will be appreciated that such alternative devices are withinthe contemplation of the invention as hereinafter described in theclaims, wherein:

1. In a well for the capture of subterranean fluids in which a powersupply located at the surface of the well drives a downhole assembly forpumping the fluid in the well to the surface through a captured splineassembly, a rod string depending from, and connected with, the powersupply and engaged with the downhole assembly; a system for theconnection and release of said rod string from said downhole assembly,said downhole assembly having a receiver, said receiver standingupwardly therefrom, said receiver encasing a captured spline assembly toprovide a torsional connection thereto.
 2. The system of claim 1,wherein said captured spline assembly being mounted in bearings withinsaid receiver to thereby permit rotation of said captured splineassembly.
 3. The system of claim 1, wherein said captured splineassembly includes a stab-in rod; a receptacle, said receptacle receivingsaid stab-in rod in rotational driving relation; said receptacledirecting rotational power to said downhole assembly; said stab-in rodconnected with said rod string for rotating said stab-in rod.
 4. In awell for the capture of subterranean fluids in which a power supplylocated at the surface of the well dries a downhole assembly for pumpingthe fluid in the well to the surface, a rod string depending from, andconnected with, the power supply and engaged with the downhole assembly;a system for the connection and release of a rod string from a downholeassembly, said downhole assembly having a receiver, said receiverstanding upwardly therefrom, said receiver housing a captured splineassembly; an on-off tool mounted in said rod string, said on-off toolbeing selectively separable to disengage said captured spline assemblyfrom said power supply as needed.
 5. The system of claim 1, wherein saidreceiver having an opening at the free end thereof, a cap, said capcovering said opening.
 6. The system of claim 5, wherein an aperture insaid cap, an extension shaft connected to said stab-in rod and passingthrough said aperture to connected with said drive string.
 7. The systemof claim 3, wherein said captured spline assembly being mounted inbearings within said receiver to thereby permit rotation of saidcaptured spline assembly.
 8. The system of claim 5, in which a powersupply located at the surface of the well dries a downhole assembly forpumping the fluid in the well to the surface, a rod string dependingfrom, and connected with, the power supply and engaged with the downholeassembly; a system for the connection and release of a rod string from adownhole assembly, said downhole assembly having a receiver, saidreceiver standing upwardly therefrom, said receiver housing a capturedspline assembly; an on-off tool mounted in said rod string, said on-offtool being selectively separable to disengage said captured splineassembly from said power supply as needed.
 9. The system of claim 6, inwhich a power supply located at the surface of the well dries a downholeassembly for pumping the fluid in the well to the surface, a rod stringdepending from, and connected with, the power supply and engaged withthe downhole assembly; a system for the connection and release of a rodstring from a downhole assembly, said downhole assembly having areceiver, said receiver standing upwardly therefrom, said receiverhousing a captured spline assembly; an on-off tool mounted in said rodstring, said on-off tool being selectively separable to disengage saidcaptured spline assembly from said power supply as needed.